Understanding Python - Part 2: Running Code

Introduction

Whether you are new to Python or not, ensuring you understand the basics will help you along the way to becoming a Python expert.

Please see the first post titled Python vs Powershell Part 1: Versioning. This first post was written in 2018 but still applies. The remaining blog posts are a continuation of this series. Lets get started!

Installation

You may have Python already installed. To check, open your terminal and type:

$ python -V

If Python is installed, you should see a version displayed below that command. If not, you may receive a command not found type of error (or something to that effect).

Depending on your operating system, you can install the Python executable from python.org. Additionally, you could use a package manager like brew.sh or chocolatey or some other variant. Either way, you must have Python installed within your environment.

There are other methods like using pyenv you can use to install different versions of python on top of each other but that is out of scope for this blog post.

Installation Check

Once Python has been installed, we should open a new terminal and type:

python -V
# or 
python3 -V

Your version of Python should be 3.7 or greater.

Python & Pip

Before we dive into using Python, we need to understand that we actually installed two executables (there are more but for this discussion we installed two); Python & pip. The Python executable (python.exe) is used to execute code, but there are several different ways to execute that code. We will go through the most common ones below.

By simply entering python in your terminal, you will run the Python interactive shell.

Interactive Shell

When in the interactive shell, we need to understand that it is basically a live session where code is run. Whatever you enter here is considered Python code; whether it’s accurate or not. Again, you gain access to the interactive shell by typing the following in your terminal:

python
# or
python3

Once in this shell, you can utilize any of the built-in functions. For example:

print
type
input
exit
# etc.

We will go into more details soon about these functions and more.

Each of these functions (above) are built-in to the Python language and are accessible by simply typing them. You don’t need to import them or do anything fancy to use them.

To exit the interactive shell, type:

exit()

Since we were in an interactive shell, we needed to call the exit function in order to return to our console (or exit the shell).

-c

Next, lets run some python directly within our console. To do this, we can use the -c parameter on the python executable.

python -c ''
# or 
python3 -c ''

The -c parameter allows us to run strings of code directly in our terminal/shell. For example:

python -c 'print("Hello World!")'

This should output Hello World in your console. Later on, this becomes extremely useful for quick snippets of code or grabbing data. For example:

python -c "import requests; print(requests.get('https://bitly.com/98K8eH'))"
# or 
python -c "import os; print(os.path.isdir('.'))"

In the next few posts, I will explain those examples in more detail.

Running Scripts

Even though we have ran our code in our console, the most common way will be using a scripts. Scripts allow us to run our code, or someone else’s, to obtain our desired outcomes. These scripts are essentially just text files, ending in .py extension, to control the flow our outcome.

Like most languages, Python is processed from top to bottom.

To run a Python script, we use the Python executable as well as the path to our script file.

python test_script.py

Lets go ahead and create a file called test_script.py in your current directory. Next, open it in Visual Studio Code.

If you don’t have Visual Studio Code, please install it.

Open up our new Python script test_script.py and add in the following:

print("Checkout the blog https://letsautomate.it.")

Now save our file and run it by calling our script:

python test_script.py

It should output the following to your console:

Checkout the blog https://letsautomate.it

Look at you! You just ran your first Python script - you are a programmer now.

What’s Next?

In the next post in this series, I will dive into the built-in primitives and methods in more detail.